Brushless permanent magnet motor or alternator with variable axial rotor/stator alignment to increase speed capability

ABSTRACT

A brushless permanent magnet electric machine with a fixed radial air gap is operated to a much higher speed than normal maximum speed by the reduction in effective magnet pole strength. Increasing the amount of axial misalignment of the permanent magnet rotor and constant velocity bearing proportionally increases the speed and reduces the torque. The permanent magnet rotor is offset axially to provide axial misalignment between the rotor magnet poles and the stator, reducing the effective magnet pole strength or flux to the stator. An integral constant velocity linear bearing is used to couple the movable rotor and the fixed position motor shaft. A thrust bearing is actuated to offset the magnetic rotor against the attractive magnetic forces toward the stator. The use of a constant velocity linear bearing allows the motor shaft, radial support bearings, position encoder, cooling fan, and output coupling to remain in a constant position while rotor position is offset.

TECHNICAL FIELD

The present invention relates to permanent magnet electric machines ofthe radial air gap type. More particularly, the present inventionrelates to permanent magnet electric machines of the radial air gap typein which the axial alignment of the rotor and stator can be varied tocontrol speed and applied torque.

BACKGROUND

Permanent magnet electric machines are known to be efficientproducers/users of rotational power. Brushless permanent magnet machineseliminate the commutator and brushes that are commonly used with anelectric controller that switches current to conductors in moreconventional electric machines. The brushless electric controllers usedin permanent magnet electric machines allow the conductor coils to belocated in stationary motor stators, which react to movement of rotorscontaining permanent magnets.

Brushless permanent electrical machines are known for their durability,controllability, and absence of electrical sparking. These factors poseproblems in commutator equipped electrical machines. When a brushlessmotor is driven by a power source, such as in vehicle regenerativebraking or wind powered generators, the motor becomes a permanent magnetalternator.

Unlike many other types of electrical machines, permanent magnetelectrical machines have a linear relationship between the product ofEMF (voltage)×current (amps) and output torque. This characteristic isideal for the traction loads of electric vehicles and other applicationswhere a linear torque/speed relationship simplifies control.

Conventional permanent magnet machines can apply high output torques upto an rpm limit called the base speed. The base speed rpm is governed bythe phenomena of permanent magnet machines building up “back-emf”electrical potentials as rotational speeds increase. The back-emf isgoverned by the magnetic gap flux density, number of winding turns, androtational speed. As the rotational speed of a permanent magnet machineincreases, the back-emf will build up until it equals the suppliedvoltage. Once the back-emf equals the supplied voltage, permanent magnetmachines will not operate any faster. This back-emf rpm limitingcharacteristic protects permanent magnet machines from the over speeddamage that is common with series wound electrical machines used invehicle applications. The back-emf base speed characteristic thatprotects permanent magnet machines also tends to limit the dynamic rpmrange.

In order to accelerate from rest or from low speeds, many electricvehicles have a fixed reduction drive ratio that is set for high torque.While such configurations provide the necessary high torque to overcomeinertia, it results in a low base speed and a limited top speed. Inaddition to a low speed, constant torque operation, it is desirable formany motor vehicles to also have an upper range of constant power, wherespeed can increase with decreased torque requirements.

There are methods by which to operate a brushless permanent magnet motoror other motor type beyond the base speed. These methods can be broadlyclassified as either those using electrical means or those usingmechanical means.

Methods of electrically enhancing speed or varying magnet flux includehigh current switching of additional phase coils or switching the waythe phase coils are connected. The costs of such contactors and theircontact wear tend to negate the advantages of a high durabilitybrushless motor. Supplemental flux weakening coils have also been usedto reduce stator flux and increase speed. This latter approach typicallyrequires contactors and increases heating effects in the stator. Othermethods can achieve higher speed operation by varying the waveform shapeand pulse angle of the applied driving current or voltage.

Other known methods include the use of DC/DC amplifier circuitry toboost the supply voltage in order to achieve a higher motor speed. Thismethod increases system costs and decreases reliability and efficiency.Such electrical approaches to increasing a motor's base speed areexemplified in U.S. Pat. Nos. 5,677,605 to Cambier et al., 5,739,664 toDeng et al. and 4,546,293 to Peterson et al.

Mechanical approaches to increasing a motor's base speed includeconfigurations that vary the radial air gap between a tapered or conicalrotor and stator. U.S. Pat. Nos. 829,975 and 1,194,645 to Lincolndisclose a conical rotor and shaft that is moved axially by a worm gearto adjust air gap and speed. U.S. Pat. Nos. 3,648,090 to Voin and4,920,295 to Holden et al. each disclose a conical rotor in analternator that is adjusted axially to vary air gap and the alternatoroutput. U.S. Pat. No. 5,627,419 to Miller discloses a conical rotor thatis moved axially to increase air gap and reduce magnetic drag on aflywheel energy storage system when the motor is not energized. In allof these patents, the rotor and stator remain engaged and changes in themagnetic air gap is achieved by small axial movements.

U.S. Pat. No. 3,250,976 to McEntire discloses motor stator coils of anAC induction motor that are moved axially between shorted andnon-shorted portions of a dual rotor to vary speed. McEntire requirescomplex multiple lead screws or ball screws to effect stator movementand a double length rotor.

U.S. Pat. No. 5,821,710 to Masuzawa et al. discloses a magnet rotor thatis split into two sections. For normal slow speed operation, themagnetic north and south poles of both rotor sections are aligned. Asmotor speed increases, centrifugal weights rotate one rotor section sothe magnetic poles have increasing misalignment with speed. The magneticpole misalignment causes a reduction in magnetic flux and back-emf,which allows the motor to run faster than normal base speed. This systemis self contained, but requires a split rotor and the centrifugalapparatus to move the one rotor segment into misalignment. The strongrepulsive forces of like magnet poles produce thrust to push the rotorsegments apart. When the poles are misaligned, the attractive forces ofunlike magnetic poles add to the centrifugal positioning force andoverride the springs used to restore the alignment position. Thesefactors add to the complicated design and effect durability, and cost.

U.S. Pat. No. 6,194,802 to Rao discloses a pancake type motor that usesa fixed axial air gap. In this type of motor the axial gap isfunctionally equivalent to the radial gap in an internal cylindricalrotor motor design with a radial air gap. The individual magnet sectorsin the rotor are mounted on spring loaded radial tracks. When the rotorrpm increases, centrifugal force causes the magnet sectors to extendradially, reducing the active area of magnet aligned with the statorcoil and reducing the back-emf. This causes the motor to run faster thanthe base speed. Rao is similar to Masuzawa et al. and Holden et al.mentioned above in the centrifugal method of activation. The design ofRao requires extensive machining of the radial magnet tracks whichincreases costs and adds to the complexity. In addition, maintaining asufficient level of balance of this magnet rotor is complicated byseveral factors. Even after the rotor is balanced with the magnets attheir inboard position, as speed increases the position of theindividual magnets is affected by difference in mass of the magnets,spring constants/rates, and sliding friction of the magnets along thetracks. Small variations in the resultant in the individual magnetpositions would have a disastrous effect on the balance at high rotorspeeds. These factors would necessarily adversely effect the ability toreduce back-emf of the motor and operate above the base speed.

DISCLOSURE OF THE INVENTION

According to various features, characteristics and embodiments of thepresent invention which will become apparent as the description thereofproceeds, the present invention provides a brushless permanentelectrical machine which includes:

a stator having a plurality of stator magnetic poles and windings forgenerating a rotating field in the stator magnetic poles, said statorhaving a central axis and a substantially uniform inner diameter;

a rotor provided with a plurality of permanent magnets at a peripheralsurface thereof and having a central axis which coincides with thecentral axis of the stator, the rotor further having a substantiallyuniform outer diameter;

a rotatable shaft upon which the rotor is coupled, the rotatable havinga central axis which coincides with the central axis of the stator; and

means for moving the rotor with respect to the stator along therotatable shaft.

The present invention further provides a method of operating a brushlesspermanent magnet electric machine beyond its normal base speed whichinvolves:

providing a brushless permanent magnet electric machine having a stator,a rotor, and a rotatable shaft upon which the rotor is coupled; and

moving the rotor with respect to the stator along the rotatable shaft.

The present invention also provides a brushless permanent electricalmachine in combination with a vehicle in which the brushless permanentelectrical machine comprises a motor for driving the vehicle, and canalso comprise a generator for a braking system of the vehicle.

The present invention further provides a brushless permanent electricalmachine in combination with a power generating system in which thebrushless permanent electrical machine comprises a generator and whichpower generating system can comprises a wind powered generator.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will be described with reference to the attacheddrawing which are given as non-limiting examples only, in which:

FIG. 1 is a graph depicting the relationship between speed and torquefor a typical air gap motor of the present invention.

FIG. 2 is a cross-sectional view of permanent magnet electric machineaccording to one embodiment of the present invention in which the rotoris fully engaged with the stator.

FIG. 3 is a cross-sectional end view of a stator, rotor and constantvelocity bearing according to one embodiment of the present invention.

FIG. 4 is an enlarged partial cut away cross-sectional view of therotor, thrust bearing and constant velocity linear bearing of FIG. 1

FIG. 5 is an end view of one embodiment of a thrust housing and leverused to adjust the axial position of a rotor according to one embodimentof the present invention.

FIG. 6 is cross-sectional view of permanent magnet electric machineaccording to one embodiment of the present invention in which the rotoris about 25% disengaged with the stator.

FIG. 7 is cross-sectional view of permanent magnet electric machineaccording to one embodiment of the present invention in which the rotoris about 50% disengaged with the stator.

FIG. 8 is a cross-sectional view of permanent magnet electric machineaccording to another embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Many applications desire the merits of a brushless permanent magnetmotor, but require operation significantly beyond the base speed. Inelectric vehicle applications, low speed operation often requiresconstant torque operation at less than the base speed for moving heavyloads, or traversing rough terrain or inclines such as hills. In manycases, high speed operation requires double or triple the base speed forcruising on level roads or developed industrial sites. In this highspeed mode, torque requirements are low and constant power operation isdesired. In constant power operation the available torque is inverselyproportional to the speed. Constant power mode in a motor equipped witha mechanism that controls back emf provides an operation that is similarto shifting gear ratios in a transmission, i.e., higher speeds aretraded for lower available torque. A motor that is able to shift fromconstant torque mode to constant power mode with speed extending beyondthe base speed according to the present invention can be utilized as amagnetic variable transmission.

Conversely, a wind power generating unit needs an alternator that willstart at minimum torque for light winds. This minimum torque exists whenthe back emf is at a minimum point. When wind speed and power increases,a maximum back emf will generate more power. By using the continuouslyvariable magnetic transmission of the present invention, a windgenerator controller can maximize the amount of energy that can becaptured from the available wind.

Since a brushless permanent magnet motor requires an electroniccontroller to switch the currents to the stator phase coils, additionalbenefits can result according to the present invention by havingindependent back emf control by the motor controller as opposed todirect control of motor centrifugal force. In these same electricvehicle applications, high speed operation will often be followed by aspeed reduction requiring regenerative braking by the motor.Regenerative braking is a control phase in which the motor acts as agenerator, slowing the vehicle and returning energy to the batteries. Byhaving the back emf adjusted by the controller (using an independentactuator) as opposed to centrifugal force, allows the motor to beshifted back into constant torque mode for optimum regenerative braking.

The present invention includes a method of axially displacing the rotorof a radial gap permanent magnet motor to reduce back emf and increasespeed above the normal base speed. The invention utilizes a permanentmagnet rotor with integral constant velocity linear bearing coupling therotor to the motor shaft. An integral constant velocity linear bearingis used to couple the movable rotor and the fixed position motor shaft,while maintaining alignment between the rotor magnet poles and the shaftposition encoder. As the rotor is offset into greater misalignment withthe stator, the magnet flux on the stator field coils is reduced,reducing the back emf that limits speed. With the rotor misaligned, themotor operates in constant power mode, where available torque isinversely proportional to speed. The rotor can be moved axially by ahydraulic, electromechanical, manual, or other actuator means connectedto a lever or other means.

The rotor and stator have a constant cylindrical shape and are wellsuited to be manufactured using low cost identical stacked laminations.The magnets are rigidly fixed to the stator by adhesive bonding or othermeans making high speed balance and durability easy to maintain. The lowfriction linear bearing allows the magnetic attraction of the rotor andstator to provide sufficient restoring force to constant torqueoperation. The linear bearing also maintains alignment between the rotormagnet poles and the shaft position encoder that synchronizes theswitching of the motor phase coils.

The present invention will now be described with reference to theattached drawings which are given as non-limiting examples only.Throughout the various figures, common reference numbers have been usedto identify common elements.

FIG. 1 is a graph depicting the relationship between speed and torquefor a typical air gap motor of the present invention. In FIG. 1 themotor torque, which increases through a minimum torque up to a maximumtorque for a given motor, is plotted against motor speed. The minimumtorque is the torque required to drive the motor when the back emf istheoretically reduced to zero. The motor's base speed, which asdiscussed above is that speed at which back emf equals applied voltage,is shown on the horizontal axis of the graph in FIG. 1. Below the motorbase speed a constant torque mode is shown. Above the base speed, and upto the motor maximum speed, a constant power mode is shown. In thislatter mode, as the torque is lowered current increases resulting in aspeed increase. The constant power mode is the motor speed addressed inthe present invention.

FIG. 2 is a cross-sectional view of permanent magnet electric machineaccording to one embodiment of the present invention in which the rotoris fully engaged with the stator. The permanent electric machinedepicted in FIG. 2 includes a housing which is formed by a com end motorhousing portion 2 and a drive end motor housing portion 4. The twohousing portions 2, 4 depicted in FIG. 2 are positioned on either sideend of stator 6 and secured in position by a plurality of tie rods 8that coupled to housing end plates 10, 12. As can be seen, since thestator 6 of the present invention is held stationary, it can beincorporated into the motor housing structure. Alternatively, the motorhousing could enclose the stator 6 by extending along the outer diameterthereof. Essentially, any suitable housing structure could be used inthe present invention, provided that provisions are made to hold thestator 6 in a fixed position. The stator windings 14 are depicted inFIG. 2 and discussed in more detail below.

Bearing assemblies 18 provided centrally in end plates 10, 12 receivemotor shaft 20 therethrough. The bearing assemblies 18 include radialball bearings 22, and can be of any conventional design. The motor shaft20 is allowed to rotate in bearing assemblies 18, but is restricted frommoving axially.

Rotor 24, having magnets 16 on the outer surface thereof, is configuredto rotate together with motor shaft 20 and move axially along motorshaft 20 as will now be described. The motor shaft 20 includes aplurality of parallel grooves 26 formed in the outer surface thereofwhich extend alone a central portion thereof. The grooves 26 have asemicircular cross-sectional shape and are configured to receive aplurality of ball bearings 28 therein. The rotor 24 includes a centralbore 30 which receives rotor sleeve 32. Rotor sleeve 32 is coupled tothe rotor 24 as discussed below and includes a plurality of parallelgrooves 34 formed in an inner surface thereof. Grooves 34 have asemicircular cross-sectional shape and are configured to receive aplurality of ball bearings 28 therein. When rotor sleeve 32 ispositioned over motor shaft 20 and grooves 26 in motor shaft 20 arealigned with grooves 34 in the rotor sleeve 32, they form channels inwhich ball bearing 28 can be held. The ball bearings 28 are containedwithin the channel formed by grooves 26 and grooves 34 by an annular cap36 on one end of the rotor n sleeve 32 and a retaining ring 38 that isattached to the opposite end of the rotor sleeve 32. An alternativearrangement could use retaining rings on both ends of the rotor sleeve32.

The rotor 24 is allowed to slide axially along motor shaft 20 with ballbearings 28 reducing friction between the rotor 24 and motor shaft 20.

FIG. 2 depicts one means for moving and positioning rotor 24 axiallyalong motor shaft 20. In FIG. 2 one end of the rotor 24 is coupled to athrust bearing assembly 40 which can move axially along motor shaft 20.Thrust bearing assembly 40 is coupled to a yoke assembly 42 that canpivot about pivot brackets 44 (one shown in FIG. 2). The yoke assembly42 is actuated (pivoted) by pivoting pivot arm 46 about the pivot axisof yoke assembly 42 as discussed in more detail with reference to FIG. 5below.

FIG. 2 depicts a hydraulic or pneumatic actuator 48 coupled to pivot arm46 for actuation thereof. FIG. 2 also depicts a biasing means, e.g.spring 50, that is coaxial with motor shaft 20 and provided on theopposite side of the rotor 24 from thrust bearing assembly 40, whichbiasing means assists in returning rotor 24 to an initial positionbefore it is pushed by thrust bearing assembly 40.

The permanent magnet electric machine of FIG. 2 includes a fan 52 thatis coupled to motor shaft 20 by fan hub 54 for rotation therewith. Fan52 is provided to cool the permanent magnet electric machine. In thisregard, the drive end of motor housing portion 4 is provided with vents56 into which ambient air can be drawn my fan 52 and forced through thepermanent magnet electric machine.

FIG. 3 is a cross-sectional end view of a stator, rotor and constantvelocity bearing according to one embodiment of the present invention.FIG. 3 shows the use of key elements 60 that can be used to secure therotor sleeve 32 to the rotor 24. In an alternative embodiment, engagingor interlocking structural elements could be formed on either or both ofthe outer surface of the rotor sleeve 32 and/or the inner surface of thebore 30 provided in rotor 24.

FIG. 3 depicts the channels 62 that are formed between grooves 34 inrotor sleeve 32 and grooves 26 formed in the motor shaft 20 when thesegrooves are aligned with one another. FIG. 3 also shows how ballbearings 28 couple motor shaft 20 and rotor 24 (via rotor sleeve 32)together to provide a constant velocity linear bearing.

As shown in FIG. 3, the rotor 24 includes a plurality of inwarddepending teeth 64 having wire coils 14 wound thereon. The teeth 64 havewidened inner facing radial surfaces 68 which are opposed tocomplementary radial surfaces of magnets 16 which are secured to theouter surface of rotor 24. The magnets 16 are attached to flat outersurfaces portions 72 of the rotor 24 by a suitable adhesive. The wirecoils 14 and magnets 16 are also shown in FIGS. 2 and 6-8. In additionto bonding the magnets 16 to the outer surface of the rotor 24, theresulting assembly can further be coaxially wrapped with a non-magneticmaterial such as carbon fibers, to ensure that the magnets willwithstand centrifugal forces as the rotor 24 is rotated at high speeds.The stator 6 and rotor 24 can be made from a plurality of laminationsthat are stacked and secured together in known manners.

FIG. 3 also shows drive end motor housing portion 4 and tie rods 8 thatextend through notches 72 provided in the outer surface of the rotor 24.

FIG. 4 is an enlarged partial cut away cross-sectional view of therotor, thrust bearing and constant velocity linear bearing in FIG. 2.FIG. 4 depicts a solid bearing 74 that is positioned between motor shaft20 and thrust bearing housing 76. Bearing 74 can be made from ansuitable soft metal such as brass, bronze, etc. or from a plasticbearing material.

FIG. 4 shows that the grooves 34 in the rotor sleeve 32 do not have tobe coextensive with the length of the rotor sleeve 32. As shown, adiscrete grouping of grooves 34 are provided at both ends of the rotorsleeve 32.

FIG. 5 is an end view of one embodiment of a thrust housing and leverused to adjust the axial position of a rotor according to one embodimentof the present invention. As shown, the yoke assembly 42 discussed abovein reference to FIG. 2 includes a pair of thrust housing lever arms 80which are fixed to and extend in parallel from torque tube 82. Thethrust lever arms 80 are welding to the torque tube 82. To assist inassembling and strengthening the yoke assembly 42 against torsionalforces, the torque tube 82 can be provided with a keyway 88 and a key88′ and the ends of the thrust housing lever arms 80 (and the pivotarm(s) 46) can included cutouts that are configured to allow ends of thethrust housing lever arms 80 (and the pivot arm(s) 46) to slide over thetorque tube 82 and engage the key 88′. Other engaging/interlockingstructural elements could also be used for this purpose.

Torque tube 82 is mounted on a pivot shaft 84 that is coupled to andsupported at opposite ends thereof to pivot brackets 44. Bearing 86 areprovided on opposite ends of torque tube 82 between the torque tube 82and pivot shaft 84. Bearings 86 can be made from an suitable soft metalsuch as brass, bronze, etc. or from a plastic bearing material. Asdepicted, pivot brackets 44 are secured to the com end motor housingportion 2 by any suitable means such as welding. Alternatively, pivotbrackets 44 can be secured to the end plate 10 as shown in FIG. 2.

A pair of shoulder bolts or screws 90 are received in aligned internallythreaded bores provided in the outer sides of thrust bearing housing 76.The shoulder bolts or screws 90 pass through elongate slots 92 providedin the free ends of thrust housing lever arms 80 and can have bearings94 thereon as show in FIGS. 5 and 4. Bearing 74, discussed above, isshown between motor shaft 20 and thrust bearing housing 76.

As shown in FIG. 5, pivot arm 46 comprises two parallel arms which arerigidly coupled to torque tube 82 and extend through a slot or passagein com end motor housing portion 2 as depicted in FIG. 2. The free endof pivot arms 46 are pivotally coupled to the movable end of actuator 48which is received therebetween. A clevis pin 96 (see FIG. 2) or otherelement providing a pivotal axis is used to pivotally couple the freeends of pivot arm 46 to movable end of actuator 48.

In an alternative embodiment, a single pivot arm 46 could be used andeither the free end thereof or the movable end of actuator 48 could havea yoke structure by which the two could be pivotally coupled togetherwith a suitable coupling pin.

FIG. 2 depicts the opposite end of the actuator 48 as being coupled tothe drive end motor housing portion 4. It is noted that the opposite endof the actuator 48 could be coupled to any structure which is fixedrelative to the permanent magnet electric machine.

FIG. 6 is cross-sectional view of permanent magnet electric machineaccording to one embodiment of the present invention in which the rotoris about 25% disengaged with the stator. FIG. 7 is cross-sectional viewof permanent magnet electric machine according to one embodiment of thepresent invention in which the rotor is about 50% disengaged with thestator.

FIGS. 2, 6 and 7 can be viewed as illustrating progressive axialmovement of the rotor 24, with the rotor 24 in FIG. 2 being in fullalignment or engagement with the stator 6, and FIGS. 6 and 7 depictingincreasing misalignment or disengagement of the rotor 24 with respect tothe stator 6.

The full alignment or engagement of the rotor 24 with the stator 6depicted in FIG. 2 will produce constant torque up to the base speed asshown in FIG. 1.

The amount of misalignment or disengagement of the rotor 24 with respectto the stator 6 depicted in FIG. 6 is approximately 25%. This amount ofmisalignment or disengagement will produce an increase in speed ofapproximately 150% of the base speed.

The amount of misalignment or disengagement of the rotor 24 with respectto the stator 6 depicted in FIG. 6 is approximately 50%. This amount ofmisalignment or disengagement will produce an increase in speed ofapproximately 200% of the base speed.

FIGS. 2, 6 and 7 are illustrative of several positions at which therotor 24 can be moved by actuator 48. It is understood that the rotor 24can be positioned in an infinite number of positions by actuator 48, soas to offer infinite control and adjustment of speed/torque.

FIG. 8 is a cross-sectional view of permanent magnet electric machineaccording to another embodiment of the present invention. The embodimentof the invention in FIG. 8 uses a linearly aligned actuator without apivot linkage. In FIG. 8 a thrust sleeve 100 is coupled to the end ofrotor sleeve 32, and the motor shaft 20 has a hollow end portion 102which receives pushrod 104. Pushrod 104 is coupled to hydraulic orpneumatic actuator 48 via a thrust bearing 106 which allows pushrod 104to rotate with motor shaft 20 and actuator 48 to move axially withoutrotating. The motor shaft 20 includes a slot 108 in one side thereofthrough which a cross pin 110 can be inserted to couple pushrod 104 tothrust sleeve 32.

In the embodiments of the invention depicted in FIGS. 2-8, when theactuator 48 is actuated, rotor 24 is pushed out of alignment with stator6 as it moves along motor shaft 20.

It an alternative arrangement, the actuator 48 can be used to pull therotor 24 out of alignment with stator 6. For Example, in FIG. 2, theactuator 48 could be turned around so that when the actuator 48 isactuated, rotor 24 moves away from the fan 52. The com end motor housingportion 2 could be lengthened together with the drive end of motor shaft20 and grooves 26 and 34 to accommodate such a configuration. Theembodiment of FIG. 8 could likewise be reconfigured so that actuator 48pulled the rotor 24 out of alignment with stator 6.

Although a hydraulic or pneumatic actuator is depicted in the figures,it is to be understood that any equivalent means could be used such as athreaded screw driven shaft, a pinion and gear assembly, a cable system,sliding actuator, etc.

Although the present invention has been described with reference toparticular means, materials and embodiments, from the foregoingdescription, one skilled in the art can easily ascertain the essentialcharacteristics of the present invention and various changes andmodifications can be made to adapt the various uses and characteristicswithout departing from the spirit and scope of the present invention asdescribed above.

What is claimed is:
 1. A brushless permanent magnet electrical machinewhich comprises: a stator having a plurality of stator magnetic polesand windings for generating a rotating field in the stator magneticpoles, said stator having a central axis and a substantially uniforminner diameter; a rotor provided with a plurality of permanent magnetsat a peripheral surface thereof and having a central axis whichcoincides with the central axis of the stator, the rotor further havinga substantially uniform outer diameter; a rotatable shaft upon which therotor is coupled so as to rotate therewith, the rotatable shaft having acentral axis which coincides with the central axis of the stator; meansfor moving the rotor with respect to the stator along the rotatableshaft without changing a radial distance between the stator and therotor.
 2. A brushless permanent magnet electrical machine according toclaim 1, further comprising a housing, the stator being held in a fixedposition relative to the housing.
 3. A brushless permanent magnetelectrical machine according to claim 1, further comprising a constantvelocity bearing which couples the rotor to the rotatable shaft.
 4. Abrushless permanent magnet electrical machine according to claim 1,wherein the brushless permanent magnet electrical machine comprises analternator.
 5. A brushless permanent magnet electrical machine accordingto claim 1, wherein the means for moving the rotor comprises at leastone of a pneumatic means, a hydraulic means, an electromechanical meansand a manual means.
 6. A brushless permanent magnet electrical machineaccording to claim 1, wherein the permanent magnets are held in fixedpositions at the peripheral surface of the rotor.
 7. A brushlesspermanent magnet electrical machine according to claim 1, furthercomprising a plurality of ball bearings between the rotor and rotatableshaft.
 8. A brushless permanent magnet electrical machine according toclaim 7, wherein the rotatable shaft is provided with a plurality ofaxial grooves for receiving the plurality of ball bearings.
 9. Abrushless permanent magnet electrical machine according to claim 5,further comprising a thrust bearing assembly which couples the means formoving the rotor to the rotor.
 10. A brushless permanent magnetelectrical machine according to claim 9, wherein the thrust bearing ispivotally coupled to the rotor.
 11. A brushless permanent magnetelectrical machine according to claim 10, further comprising a pivotallinkage coupling the means for moving the rotor to the thrust bearing.12. A brushless permanent magnet electrical machine according to claim9, wherein the thrust bearing is coupled to the rotor for axial movementtherewith.
 13. A brushless permanent magnet electrical machine accordingto claim 12, further comprising a pushrod coupling the means for movingthe rotor to the thrust bearing.
 14. A method of operating a brushlesspermanent magnet electric machine beyond its normal base speed whichcomprises: providing a brushless permanent magnet electric machinehaving a stator with a substantially uniform inner diameter, a rotorwith a substantially uniform outer diameter, and a rotatable shaft uponwhich the rotor is coupled so as to rotate therewith; and moving therotor with respect to the stator along the rotatable shaft withoutchanging a radial distance between the stator and the rotor.
 15. Amethod of operating a brushless permanent magnet electric machine beyondits normal base speed according to claim 14, wherein the permanentmagnet electric machine includes a housing and the method furthercomprises securing the stator in a fixed position relative to thehousing.
 16. A method of operating a brushless permanent magnet electricmachine beyond its normal base speed according to claim 14, wherein thebrushless permanent electrical machine comprises an alternator.
 17. Amethod of operating a brushless permanent magnet electric machine beyondits normal base speed according to claim 14, wherein the step of movingthe rotor with respect to the stator involves manipulating a pivotalmechanism.
 18. A method of operating a brushless permanent magnetelectric machine beyond its normal base speed according to claim 14,wherein the step of moving the rotor with respect to the stator involvesmanipulating a pushrod coupled to the rotor.
 19. A brushless permanentmagnet electrical machine according to claim 1 in combination with avehicle in which combination the brushless permanent electrical machinedrives the vehicle.
 20. The combination of claim 19, wherein thebrushless permanent magnet electrical machine further generates avoltage when the vehicle brakes.
 21. A brushless permanent magnetelectrical machine according to claim 1 in combination with a powergenerator system in which combination the brushless permanent magnetelectrical machine comprises a generator.
 22. The combination of claim21 wherein permanent magnet electrical machine comprises a wind poweredgenerator.